Blade holder for a doctor and a method for using the doctor

ABSTRACT

A blade holder for a doctor and method for using the doctor is disclosed, in which in the front part there is a throat or similar for the doctor blade of the doctor and which blade holder has loading members connected thereto to press the doctor blade against the surface to be doctored. The blade holder further includes a relatively stiff, slightly flexible frame plate, which incorporates the attachment flange. The blade holder also includes loading devices for directing the force of the loading members onto the frame plate at a distance from the attachment flange, to bend the frame plate and thus press the doctor blade against the surface to be doctored.

TECHNICAL FIELD

The present invention relates to a blade holder for a doctor, in whichin the front part there is a throat or similar for attaching the doctorblade of the doctor and which is intended to be attached from its rearpart to the frame by means of an attachment flange, and which bladeholder has loading members connected to it to press the doctor bladeagainst the surface to be doctored. The invention also relates to amethod for using the doctor.

BACKGROUND OF THE INVENTION

In conventional doctors, there are principally two kinds of bladeholder. The first kind are fixed, i.e. rigid blade holders. The secondkind, on the other hand, are flexible blade holders. The flexible bladeholders can be further divided more precisely into flexible andprofiling blade holders. Conventional profiling (flexible) doctorsinclude a blade carrier with a blade holder fitted rotatably to it.Usually, the rotation is implemented by means of bearings, which extendfrom one end of the doctor to the other. In addition, a doctor blade isfitted to the blade holder, to doctor the surface of a roll or a similarmoving surface. In order to alter the position of the doctor blade andto create an adequate blade load, the blade holder is rotated inrelation to the blade carrier, by means of loading members. Normally,two loading hoses between the blade carrier and the blade holder, oneach side of the bearings, are used as the loading members. Particularlyin paper machines, there are numerous such doctors in several differentpositions. The doctor beam too, with its possible loading members, canalso be used to create a basic load on the doctor blade. In rigid bladeholders, it is precisely the doctor beam only that loads the doctorblade.

Mainly on account of the bearings, known doctor-blade-holdercombinations are extremely complicated and thus also expensive. Thebearings contain many moving parts, which wear in use and thus requiremaintenance. Looseness in the bearings may also have an adverse effecton the doctoring result. A fixed blade holder transmits all the forcefrom the doctor beam to the surface of the roll being doctored. In thiscase, there is no way of compensating for force variations, installationfaults, or similar caused by the bearings or other structures. Profilingand flexible blade holders in general can compensate slightly for thesevariations, so that the bearing system used in the blade holder is notquite so critical. On the other hand, looseness in the bearings andother structures in the blade holder will cause such detrimentalvariations. The blade angle of the doctor blade also changes as thedoctor blade wears, hampering the operation of the doctor and shorteningthe doctor blade's service life. In addition, metallic blade holderstogether with the other components add considerably to the total weightof the doctor. Service costs are further increased by the severaldifferent blade-holder models, each of which requires differentspare-parts and tools.

SUMMARY OF THE INVENTION

The invention is intended to create a blade holder for a doctor, whichcontains fewer components than previous known blade holders and which ismore economical to manufacture. The invention is also intended toachieve a method for using the doctor, which method is simpler to useand easier to control.

The characteristic features of this invention are provided by a bladeholder for a doctor, in which in the front part there is a throat forattaching the doctor blade of the doctor and which is intended to beattached by its rear part to the frame by an attachment flange. Theblade holder has loading members connected thereto to press the doctorblade against the surface to be doctored, and is characterized in thatthe blade holder further includes a relatively stiff, slightly flexibleframe plate, which incorporates the attachment flange, and loadingdevices for directing the force of the loading members on the frameplate at a distance from the attachment flange, in order to bend theframe plate and thus press the doctor blade against the surface to bedoctored.

The frame plate may be manufactured from a composite material to form acomposite piece and reinforcing fibers of the composite piece areoriented in such a way, that the composite piece is relatively stiff inthe lateral direction of the doctor blade and essentially flexible inthe longitudinal direction of the doctor blade.

In one arrangement the loading members include one loading hose, whichis set between the frame plate and the loading devices, in order toalter the distance between them. The loading devices include a backingplate, which is attached, by a connector at a distance from the frameplate, and the loading members are arranged to affect the distancebetween the rear parts of the frame plate and the backing plate. Theloading members may include a protruding piece adapted to be attached toframe, which extends for a distance from the attachment flange, and inwhich space for the loading members is arranged.

A method for using a doctor, in which there is a throat in the frontpart of the blade holder of the doctor for attaching the doctor blade ofthe doctor and the blade holder is attached from its rear part to theframe by an attachment flange, and the blade holder has loading membersconnected to it, by means of which the doctor blade is pressed againstthe surface to be doctored, is characterized in that the blade holder isformed of a relatively stiff, slightly flexible plate forming a frameplate, which is bent by a force, which is directed at a distance fromthe attachment flange, so that a force pressing against the surface iscreated in the doctor blade. The force is transmitted with the aid of astiff blacking plate from a rear part to a front part of the frame plateso that the stiff backing plate is attached by its front part to theframe plate and its rear part is at a distance from the frame platedetermined by the loading members. Loading members are located at theend of the protruding piece attached to the attachment flange to actdirectly on the front part of the frame plate.

A blade holder according to the invention has no bearings or othermoving parts at all, instead, the structural components are fitted, toeach other. This substantially simplifies the construction of the bladeholder. Sufficient movement is created in the doctor blade by means theflexing of the structural components, which is created by means ofloading members. In addition, the properties of the blade holder can beadapted by means of the selection of the manufacturing materials. At thesame time, the weight of the blade holder is reduced and there isgreater freedom of design. The method according to the invention permitsthe accurate loading of the doctor in a simple, but comprehensivemanner.

In the following, the invention is disclosed in detail with reference tothe accompanying drawings showing some applications of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a side view of the blade holder of a doctor according tothe invention, arranged in connection with a roll,

FIG. 1b shows part of an adapted blade holder according to theinvention,

FIG. 1c shows part of the frame plate of an adapted doctor according tothe invention and of its attachment flange,

FIG. 2a shows a side view of a partial cross-section of another bladeholder of a doctor according to the invention, arranged in connectionwith a roll,

FIG. 2b shows a variation of the blade holder of FIG. 2a.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1a shows one blade holder of a doctor according to the invention.The blade holder has a throat 7, in which the doctor blade 4 is placedfrom the side of the doctor. Doctor blade 4 itself is, as such,conventional, and, in this case, doctor blade 4 also includes anattachment spring 6. In some doctor blades, there may also be rivets 6′or similar, for which a space 11 (FIG. 1b) might be left in throat 7.

By means of doctor blade 4, some moving surface, such as the surface ofthe roll 8 of a paper machine, is doctored according to FIG. 1a. Theblade holder according to the invention may also be freely in otherpositions than those shown here. The blade holder is attached by anattachment flange 12 of its rear part. The attachment is examined ingreater detail in connection with FIG. 1c.

The blade holder according to the invention includes a quite stiff,slightly flexible frame plate 1. This frame plate 1 extends essentiallyover the entire width of the paper machine and contains the saidattachment flange 12. In addition, the blade holder includes devices 13for directing the force creating by the loading members 5 onto frameplate 1, at a distance from the attachment flange 12. This force is usedto bend frame plate 1 and thus press doctor blade 4 against the surfaceto be doctored. In the figures, the same reference numbers are used forcomponents that are functionally similar.

In this case, the plate is sufficiently flexible to be able to be bentby means of the loading members. However, the plate is also sufficientlystiff for it to scarcely bend under its own weight, but to return to itsoriginal state when the force of the loading members in removed. Inaddition, the distance to be moved is set to be such that the plate canbe made to bend as desired by using the loading members. In practice,the force is moved closer to the front part of the blade holder.

In FIG. 1a, frame plate 1 containing attachment flange 12 is underneath.The other plate is a backing plate 2, the function of which is describedlater in greater detail. In addition, the plates are connected at theirfront parts 1′ and 2′ by means of a connector 3 and at their rear parts1″ and 2″ at a short distance from each other by means of loading member5. Connection 3 is permanently attached to the plates and may be even apivot. However, in any event, connector 3, together with doctor blade 4,retention spring 6 and throat 7 forms a rigid support between theplates. Thus, there are no moving parts requiring maintenance in theblade holder. In addition, the general construction of the blade holderis simpler than previously.

The doctor blade is set and loaded against the surface to be doctoredveritably with the aid of the loading members. Generally, the loadingmembers are set between the frame plate and the devices. In addition,the loading members are arranged to alter the distance between the frameplate and the devices. In the blade holder according to FIG. 1a, theloading members 5 are arranged to affect the distance between the rearparts 1″ and 2″ of the plates. In addition, frame plate 1 is moreflexible than backing plate 2, so that the movement of the loadingmembers 5 is converted into movement in doctor blade 4. Backing plate 2,on the other hand, can be quite rigid, as frame plate 1 acts as a kindof spring. Frame plate 1 is selected in such a way that its direction ofreturn is against the effect of loading devices 5. When the pressure ofloading members 5 drops, frame plate 1 then flexes, pressing the entireblade holder with doctor blade 4 against roll 8. Further, the blade loadof the doctor blade is altered by adjusting the force of the loadingmembers. In FIG. 1a, the blade holder is in a loaded state. Byincreasing the pressure of the loading members, the frame plate bendsupwards, and the doctor blade will rise off the surface of the roll (notshown).

The blade holder is manufactured from plates, which simplifies themanufacture of the blade holder. In addition, frame plate 1 ispreferably manufactured from a composite material. In that case, theflexing properties of the frame plate can be easily influenced by thesuitable orientation of the reinforcing fibres. At the same time, theweight of the blade holder is reduced considerably. In addition,composite materials are easily shaped. Alternatively, both plates aremanufactured from a composite material. Further, both plates and theconnector can be manufactured as a single composite piece. In that case,the blade holder can be manufactured at one time, for example, using thepultrusion method.

The orientation of the reinforcing fibres in composite pieces is veryimportant. In a blade holder according to the invention, the reinforcingfibres are preferably oriented in such a way that the composite piecesare relatively stiff in the lateral direction of the doctor blade andessentially flexible in the longitudinal direction of the doctor blade,i.e. the lateral direction of the roll. The effect of the loadinigmembers is then transferred as fully as possible to the doctor blade. Onthe other hand, a blade holder that is flexible in the longitudinaldirection of the doctor blade adapts very well, for example, to theshapes of a curved roll. Correspondingly, if special loading devices areused, it is possible to create a desired loading profile in the doctorblade. These properties can permit even a single type of holder to bemanufactured and used in different positions. Besides the selection ofthe reinforcing fibres, the dimensions of the plates can be used toaffect the properties of the blade holder, which can be arranged asdesired.

According to FIG. 1a, loading members 5 include only a single loadinghose 5′, which is set between the rear parts 1″ and 2″ of the plates Theloading hose is then well protected between the plates, permitting theuse of a conventional loading hose. The length of the working movementof the loading hose also affects the length of the movement of thedoctor blade. Deviating from FIG. 1a, the direction of movement of theloading hose can be chosen differently, when the operation of the doctorcan be set as desired. For example, by rotating the direction ofmovement of the loading hose 45° clockwise, the doctor blade can beturned even more effectively. The blade holder can be attached simplyfrom frame plate 1. The attachment can be made to the frame 9 of thedoctor, or even directly to the frame of the paper machine. On accountof its lightness, blade holder manufactured from composite material doesnot need a separate frame, because it does not bend under its ownweight. It is also possible to use an adapter piece 9′ (FIG. 1a) in theattachment. The attachment flange can also incorporate quick-releasedevices, making it simple to change the entire blade holder. Thequick-release can be according to FIG. 1c, in which the rear part 1″ offrame plate 1 is attached by means of rivets 10 to the throat 7′ inframe 9, in the same manner as the doctor blade. In that case, if theblade holder breaks, the resulting maintenance shutdown will beconsiderably shorter than usual.

FIGS. 2a and 2 b show two variations of another embodiment of a bladeholder according to the invention. The operating principle correspondsto that described above, but in these a direct loading is used. Here,devices 13 include a to frame 9 attached protruding piece 14, whichextends a short distance from attachment flange 12. Protruding piece 14is essentially rigid and forms a loading support. Frame plate 1 andprotruding piece 14 are attached directly to, for example, frame 9 ofthe paper machine. In addition, there is space in protruding piece 14for loading member 8, so that loading hose 5′, which is used as theloading member, will remain firmly in place. In this case too, the bladeholder includes a second plate forming a cover plate 15, which is moreflexible than frame plate 1. Here, the cover plate has a secondary forceeffect. In addition, the cover plate supports and protects the bladeholder and partly also controls the operation of the blade holder. Bothplates are dimensioned in such a way that when the loading member isoperated, the doctor blade presses against the surface to be doctored,the blade angle remaining, however, unaltered, despite the wear of theblade. Thus, the blade can be worn to become narrower than previously,without detrimental vibration or so-called biting of the doctor blade.

In the variation of FIG. 2a, frame piece 14 is metal. In addition, frameplate 1 and cover plate 15 are attached from their front parts 1′ and 2′to a special holder, to which doctor blade 4 is attached. In practice,the holder also forms a connector 3. The combined operation of frameplate 1 and cover plate 15 support doctor blade 4 sufficiently andsimultaneously keep the blade angle constant. FIG. 2b shows anothervariation of the blade holder. Here, frame plate 1, cover plate 15, andconnector 3 form a throat 7 for doctor blade 4. In addition, connector 3is made of a flexible material and permits a change in angle between theplates. Gluing, for example, can be used to secure the connector.Protruding piece 14 can also be manufactured as a composite piece,according to FIG. 2b. This results in a further reduction in the totalweight of the blade holder. The flexible composite pieces can also bemanufactured as a unified, closed structure, inside which the protrudingpiece and the loading hose are placed (not shown). Such a blade holderis compact and its components are well protected.

Advantages are gained from the simple construction of the blade holder,especially in paper machines, in which the rolls used are very wide. Thepossibility to vary the flexing properties is also important, especiallyin doctors used with curved rolls. The use of a single kind of bladeholders also helps to reduce service costs, as does the simpleconstruction of the blade holder. In addition, a blade holder accordingto the invention is cheaper to manufacture than an ordinary metal bladeholder and suits different kinds of doctor blades. Manufacturing costsare also reduced by the lack of a need for machining, as the compositepieces are ready to use, even without machining.

Although the invention has been described by reference to specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but that it have the full scope defined by thelanguage of the following claims.

What is claimed is:
 1. A blade holder for a doctor, in which in the frompart there is a throat for attaching the doctor blade of the doctor andwhich is intended to be attached by its rear part to a frame by anattachment flange, and which blade holder has loading members connectedthereto to press the doctor blade against the surface to be doctored,characterized in that the blade holder further includes a relativelystiff, slightly flexible frame plate, which incorporates the saidattachment flange, and loading devices for directing the force of theloading members on the frame plate at a fixed distance from theattachment flange, in order to bend the frame plate and thus press thedoctor blade against the surface to be doctored.
 2. A blade holderaccording to claim 1, characterized in that the frame plate ismanufactured from a composite material to form a composite piece.
 3. Ablade holder according to claim 2, characterized in that reinforcingfibers of the composite piece are oriented in such a way, that thecomposite piece is relatively stiff in the lateral direction of thedoctor blade and essentially flexible in the longitudinal direction ofthe doctor blade.
 4. A blade holder according to claim 1, characterizedin that the loading members include one loading hose, which is setbetween the frame plate and the loading devices, in order to after thedistance between them.
 5. A blade holder according to claim 1,characterized in that the loading devices include a backing plate, whichis attached, by a connector at a distance from the frame plate, and thatthe loading members are arranged to affect the distance between the rearparts of the frame plate and the backing plate.
 6. A blade holderaccording to claim 1, characterized in that the loading members includea protruding piece adapted to be attached to frame, which extends for adistance from the attachment flange, and in which space for the loadingmembers is arranged.
 7. A method for using a doctor, in which there is athroat in the front part of the blade holder of the doctor for attachingthe doctor blade of the doctor and the blade holder is attached from itsrear part to the frame by an attachment flange, and the blade holder hasloading members connected to it, by means of which the doctor blade ispressed against the surface to be doctored, characterized in that theblade holder is formed of a relatively stiff, slightly flexible plateforming a frame plate, which is bent by a force, which is directed at afixed distance from the attachment flange, so that a force pressingagainst the surface is created in the doctor blade.
 8. A methodaccording to claim 7, characterized in that the force is transmittedwith the aid of a stiff blacking backing plate from a rear part to afront part of the frame plate so that the stiff backing plate isattached by its front part to the frame plate and its rear part is at adistance from the frame plate determined by the loading members.
 9. Amethod according to claim 7, characterized in that the attachment flangeis equipped with a protruding piece at the end of which the loadingmembers are located to act directly on the front part of the frameplate.